Methodology of true pulmonary blood volume determination.

THE pulmonary blood volume may be defined as the volume of blood interposed between the pulmonary artery, at the pulmonary valve, and the left atrium. The volume has been measured either on a relative or on an absolute basis, that is, by measurement of changes in pulmonary blood volume or by determination of the actual volume. The former method includes determination of lung volumes, or of pulmonary compliance, use of radioactive tracers to detect changes in radioactivity over specific areas of the lung, and use of a critically balanced teeter board.' Absolute values for pulmonary blood volume have generally been obtained by the indicatordilution technique in which the indicator is introduced into the right side of the heart and sampled from the systemic arterial tree.2 4 The volume measured varied with the injection site, that is, the peripheral venous tree, the right heart, or the pulmonary artery. The results have been analyzed by the StewartHamilton,2 3 the Bradley equilibration,5 and the Newman exponential downslope6 methods. Only the first of these approaches2 3 has proven to be applicable to the determination of pulmonary blood volume.' However, the blood volume so defined still varies with the exact injection and sampling sites employed. More recently Giuntini and associates7 described a precordial radioactive method for determining true pulmonary blood volume. The development of transseptal left heart catheterization has permitted more exact